1. Field of The Invention
The present invention relates to a diamond crystal exhibiting excellent characteristics for electronic materials, a tool, hardness measurement, and the like, and a method of manufacturing the same.
2. Description of The Prior Art
Diamond has unique physical properties, e.g., a very high thermal conductivity, a high hardness, a high wear resistance, and a very high refractive index, a very high reflectance, and electrical conductivity. For this reason, diamond is used for a hardness meter, tools, abrasive materials, electronic materials, and the like as well as for ornament. Recently, application of the diamond to semiconductor materials has been considered.
As one of the excellent electrical characteristics of the diamond, a stable negative electron affinity is known. That is, the diamond tends to emit electrons from its surface. A great deal of attention has been paid to a cold cathode as one of electronic parts to which the above characteristic is applied (NIKKEI SCIENCE, December Issue, 1992, pp. 129-130). As another application of this characteristic, the use of a diamond crystal as a probe of an apparatus such as an AFM (Atomic Force Microscope) or STM (Scanning Tunnel Microscope) which is designed to analyze the atomic structure of a surface of a substance has been considered.
In diamond, the concentration of atoms and the atomic arrangement vary depending on different crystal planes, and hence the physical properties also differ. It is known that the (111) plane has a negative electron affinity, which is advantageous for the above applications. It is also known that emission of a larger number of electrons occurs at a sharp portion than at a flat portion because an electric field more easily concentrates on the sharp portion.
Chemical vapor deposition methods (CVD methods) of synthesizing a diamond from a vapor phase at a low pressure have been recently studied and developed, and CVD methods of various schemes have been tried. In consideration of the above applications, it is necessary to arbitrarily control the crystal orientation and shape of diamond synthesized by a CVD method.
A few techniques of controlling the crystal direction of diamond synthesized by a CVD method are known. One of the techniques is called an epitaxial growth method. According to this method, as a substrate for precipitation of a diamond, a diamond substrate or a substrate consisting of limited materials (e.g., silicon carbide, silicon, cubic boron nitride, or nickel) is used. With the use of such a substrate, a diamond can be oriented in the same direction as the crystal direction of the substrate ("Surface Science", Mar. 10, 1994, Vol. 15-2, pp. 91-95). Another method is disclosed in Japanese Unexamined Patent Publication No.2-160695. In this method, a source gas containing an organic compound is activated on a monocrystalline copper substrate to precipitate a diamond as a hexahedral to octahedral single crystal whose (111) plane is grown to be parallel to the substrate.
By using these methods, diamonds oriented on the (111) plane can be synthesized. However, in order to form the diamond into a shape suitable for a cold cathode or an analyzer for the atomic structure of a substance surface as applications, the resultant diamond crystal must be partially sharpened to cause an electric field to concentrate thereon.
For example, the following methods, although they are not designed for diamond, are known as methods of manufacturing a sharp emitter on a portion of a field emission type cold cathode as a type of cold cathode manufactured by using monocrystalline silicon: (1) a method using vacuum deposition; (2) a method using anisotropic etching; (3) a method using a film deposition shape; and (4) an ion milling method ("Electronic Industry Monthly Report", December, 1990, Vol. 32-12, pp. 23 to 25). Methods (1) to (3) of these methods are designed to form an emitter on a silicon substrate by vapor deposition and hence cannot be applied to a diamond sharpening process. Method (2) poses difficulty in anisotropic etching of diamond and can be applied only to a single crystal. Since it is impossible, at present, to synthesize a diamond single crystal having a large area, this method cannot be used. Method (4) is a method of isotopically processing a crystal by irradiating an ion beam regardless of the crystal direction. It is, however, difficult to sharpen diamond by using ions, and it takes much time for such a process. In addition, delicate energy control is required for an ion beam. Therefore, it is difficult to put this method into practical use.